Linear motors have been proposed which are used in factory automation (FA) equipment, for example, for driving a stage of a semiconductor exposure apparatus or a liquid-crystal exposure apparatus or feeding a table of a machining tool, aiming at high-speed feeding and machining and high-precision processing. A linear motor employing a so-called “dual cooling mechanism” is known as this type of linear motors. Related conventional technologies include a technique described in Japanese Patent No. 3459978.
A linear motor described in Japanese Patent No. 3459978 includes a magnet that forms a field pole, a coil that forms an armature arranged facing the magnet via a magnetic gap, a shell that contains the coil therein with a predetermined gap and cools down the coil by passing a refrigerant through the gap, and an outside cover that contains the shell therein with a predetermined gap and cools down the shell by passing the refrigerant through the gap. With this configuration, the refrigerant (in a low-temperature condition) is first introduced in the longitudinal direction of the coil through a first outside main channel formed between the coil and the shell, and then the refrigerant flows in the lateral direction through a second outside main channel formed between the shell and the outside cover after passing through the first outside main channel. The refrigerant is then supplied to the inside of the shell through the second outside main channel, and discharged to outside from a discharge tube flowing in the lateral direction along the surface of the coil (in a highest-temperature condition).
The conventional technique can suppress an increase in the surface temperature to some extent by the refrigerant cooling. However, when an increase of thrust force is aimed with a similar linear motor size, an increase in the surface temperature of the armature due to heat generated from the coil when applying a current to the armature to increase the thrust force can be hardly avoided, which causes a problem in enhancing cooling efficiency.